First, Congrats on finding a GREAT CAR!!!
You are a lucky man to find a 67 L79 that is that unmolested and well documented. Is it the original paint?
Second, the stamps, locations and broach marks look 100% Legit to me. To the extent the stamps are not identical, that is common. 65 and 66 Kansas cars used a much taller font on the trans than on the block (havenít found an original unrestored 67 Kansas car to check yet). Some 66 Fremont cars are the same way. I went out and checked my 66 Baltimore car and it has the same style and size characters on the block as your block (I havenít put it on the lift to try to see the trans stamp on it yet). And I have a 67 Baltimore L-78 block that has the exact same style and size VIN characters as your block.
Also, someone correct me if I'm wrong, but I had understood that Baltimore had more than one assembly line running simultaneously, so there would have been multiple sets of stamps in that plant anyway. I'm sure they didn't throw away an entire set of dies every time one digit wore out, so individual dies would logically have been replaced at various different times, and could have been with different fonts. And there is no question that differing dies have been seen even within a single stamping on many documented original blocks. For example, look at the two adjacent 2's in the pic of your engine assembly date stamp (one wide, one skinny). That was of course done at the engine plant, but it makes the point all the same.
It is correct that all L79ís should be VIN-stamped regardless of assembly plant. (Every Chevelle engine 327-300HP or higher was supposed to be VIN-stamped at every plant. I have heard that by 1967 even low-po V8ís were supposed to be VIN stamped, but Iíve never checked a 67 283 or low-horse 327 to see if that is true or not.)
I am also a firm believer in the "common sense" factor. If your trans vin was only uncovered after your removed the trans from the car, and it was covered in dirt before you wiped it off (as it looks like was the case in the pic), and if all the bolts were cruddy, then I wouldn't be too worried about it!! Decades of grease and dirt accumulation just cannot be duplicated to fool someone who performs a careful personal inspection of a car (as long as that someone has any meaningful experience with an old greasy car)!
So I don't think you have anything to be worried about as long as everything else (casting dates and #'s) checks out. Especially when you have matching documentation as you appear to have! Jeff